Electro-optical inspection

ABSTRACT

A method and apparatus for inspecting workpieces for rapid and accurate determination of dimensions and the like. The equipment is electro-optical in nature and there is no contact between the inspecting elements and the workpiece under inspection. An electro-optical sensor is utilized which includes a light source for illuminating at least one edge of a workpiece, a lens for forming an image of the illuminated edge, and an array of photosensitive elements, such as photodiodes, capable of producing an electrical signal in response to light incident thereon. The light, including the edge image, is impinged upon the array and the electrical signals produced correspond to the portion of the edge, its shape, etc. The signals can be rapidly analyzed to provide a determination of a dimension such as length, squareness, curvature, and the like.

This application is a continuation of application Ser. No. 815,270 filedDec. 24, 1985, now abandoned, which is a continuation of applicationSer. No. 531,216, filed Aug. 26, 1983, now abandoned, which is adivision of Ser. No. 269,614, filed June 2, 1981, now U.S. Pat. No.4,576,482, which is a continuation of Ser. No. 073,226, filed Sept. 7,1979, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates a method and apparatus for inspecting workpiecessuch as camshafts, crankshafts, engine valves, automotive body panels,and the like. In one aspect, this invention relates to such inspectionfor the purposes of determining a dimension of the workpiece such aslength, thickness, squareness, curvature, and the like. In particular,the invention relates to such apparatus and method capable of very rapidand accurate measurements and more particularly to such measurementsmade "on the fly", that is, when the object is moving. The inventionfurther relates to such method and apparatus which utilizes anelectro-optical type of gage and in which there is no physical contactbetween the workpiece and the gage.

Many devices are known to be suitable to inspect workpieces for thepurpose of determining dimensions and the like. While some are rapid,some are reliable, some are accurate and some are capable of measuringdimensions of complex workpieces such as a crankshaft, it is an objectof the present invention to provide methods and apparatus foraccomplishing all of these objects simultaneously.

BRIEF SUMMARY OF THE INVENTION

The foregoing and other objects which will be apparent to those ofordinary skill in the art are achieved in accordance with the presentinvention which in one embodiment comprises an electro-optical sensorapparatus for sensing a dimension of a workpiece, the sensor apparatuscomprising light source means for illuminating at least one edge of aworkpiece, lens means for forming an image of the illuminated edge ofsaid workpiece, and a photodiode array comprising a plurality ofphotodiodes capable of producing an electrical signal in response tolight incident thereon, said array being positioned to receive the imageof an illuminated edge of a workpiece.

In a further embodiment, the invention provides an apparatus forinspecting an elongate workpiece, the apparatus comprising means formounting an elongate workpiece for rotation about its longitudinal axis,means for rotating a mounted workpiece, an electro-optical sensor unitfor sensing the position of a portion of a mounted workpiece, saidsensor unit comprising a light source means for illuminating an edge ofthe portion of a mounted workpiece, a lens means for forming an image ofthe illuminated edge of a mounted workpiece, and a photosensitive arraycomprising a plurality of light sensitive elements capable of producinga signal in response to light incident thereon, the array beingpositioned to receive the image of an illuminated edge of a mountedworkpiece and means for analyzing the signals from said light sensitiveelements to determine a dimension of the portion of the workpiece.

The apparatus just described has particular application to theinspection of camshafts, crankshafts, engine valves and other machinedelongate workpieces where rapid and accurate measurements of dimensionare important, particularly when close tolerances are required, such asfor increased fuel economy in internal combustion engines. In thisevent, the apparatus is preferably provided with means for automaticallytransferring the workpiece in question from a production line conveyorsystem on which the workpiece is normally moved, into an inspectionlocation in the apparatus and, after inspection, back to the conveyorsystem. It will be readily appreciated that in a production lineinspection system such as this, speed is essential.

In a further embodiment, the invention provides apparatus for inspectinga generally planar workpiece such as an automobile body panel, theapparatus comprising means for conveying said workpiece to an inspectionlocation, means for positioning a workpiece in a predetermined referenceposition in said inspection location, electro-optical sensor means forsensing the positions of a plurality of edge portions of a workpiecepositioned in said inspection location, said sensor means comprising alight source means for illuminating a plurality of edge portions of apositioned workpiece, lens means for forming an image of saidilluminated edge portions, and a plurality of photosensitive arrays,each array comprising a plurality of light sensitive elements capable ofproducing an electrical signal in response to light incident thereon,each array being positioned to receive an image of a respectiveilluminated edge portion of a positioned workpiece, and means foranalyzing the signals from the light sensitive elements to determine adimension of the workpiece.

A first embodiment of a method of the invention comprises a method forsensing a dimension of a workpiece comprising illuminating at least oneedge of a workpiece, forming an image, by a lens means, of theilluminated edge of the workpiece, and impinging the image of anilluminated edge of the workpiece upon a photodiode array comprising aplurality of photodiodes capable of producing an electrical signal inresponse to light incident thereon.

A second embodiment of a method of the invention comprises inspecting anelongate workpiece, the method comprising mounting an elongate workpiecefor rotation about its longitudinal axis, rotating the mountedworkpiece, illuminating an edge of a portion of a mounted workpiece,forming an optical image of the illuminated edge of the workpiece,detecting the image of the illuminated edge of the mounted workpiece ona photosensitive array of light sensitive elements capable of producinga signal in response to light incident thereon, and analyzing thesignals from said light sensitive elements to determine a dimension ofthe portion of the workpiece.

The method just described has particular application to the inspectionof crankshafts, camshafts, engine valves and other elongate workpieceswhere, as mentioned above, rapid and accurate measurements of dimensionare important.

In a further embodiment, the invention provides a method for inspectinga generally planar workpiece comprising conveying said workpiece to aninspection location, positioning said workpiece in a predeterminedreference position in said inspection location, illuminating a pluralityof edge portions of a position workpiece, forming an image, by lensmeans, of said illuminated edge portions, impinging each of the imagesonto a photosensitive array, each array comprising a plurality of lightsensitive elements capable of producing an electrical signal in responseto light incident thereon, and analyzing the signals from the lightsensitive elements to determine a dimension of the workpiece.

There follows a detailed description of preferred embodiments of theinvention, together with accompanying drawings. However, it is to beunderstood that the detailed description and accompanying drawings areprovided solely for the purpose of illustrating preferred embodimentsand that the invention is capable of numerous modifications andvariations apparent to those skilled in the art without departing fromthe spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a first embodiment of the invention asapplied to camshaft inspection;

FIG. 2 is a diagrammatic end elevation view of a portion of FIG. 1;

FIG. 3 is a diagrammatic plan view of a portion of FIG. 1;

FIG. 4 is a graphical representation of an electrical signal output froma plurality of photodetectors of the device shown in FIG. 1;

FIG. 5 is a diagrammatic end elevation view of a device of the typeshown in FIG. 1 and showing a conveyor and housing not shown in FIG. 1.

FIG. 6 is a diagrammatic end elevation view of a portion of a furtherembodiment of the invention;

FIG. 7A is a diagrammatic end elevation view of a further embodiment ofthe invention as applied to the inspection of crankshafts;

FIG. 7B is a diagrammatic end elevation view of a detail of FIG. 7A.

FIG. 8 is a diagrammatic perspective view of a further embodiment of theinvention involving the inspection of engine valves;

FIG. 9 is a diagrammatic perspective view of a further embodiment of theinvention involving the inspection of a transmission pump vane;

FIG. 10A is a diagrammatic side elevation view of a further embodimentof the invention involving the use of a transparent conveyor belt;

FIG. 10B is a diagrammatic plan view of a further embodiment of theinvention involving the use of a conveyor belt having less width thanthe width of the object undergoing inspection;

FIG. 10C is a diagrammatic end elevation view of FIG. 10B;

FIG. 11 is a diagrammatic perspective view of a further embodiment ofthe invention involving the inspection of an automobile door panel;

FIG. 12 is an electrical schematic diagram of a circuit for performingan analysis of the electrical signals of the type graphicallyillustrated in FIG. 4; and

FIG. 13 is a graphical representation similar to that of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The embodiment of the invention depicted in FIG. 1 provides a new typeof inspection gage for inspecting automotive and other camshafts. Theneed for such a gage is widespread due to the ever increasingrequirements for improved engine omissions and fuel economy. Far morestringent requirements in the quality of camshafts result and 100%inspection of all pertinent variables is the only answer.

In order to achieve true 100% inspection of all camshafts on an economicbasis, the invention here described appears to be the only realisticmethod of achieving this goal. In addition, the invention is also of useon crankshafts and other parts.

The invention here disclosed can inspect a typical automotive camshaftin approximately 20 seconds for:

(1) Base circle runout

(2) Contour 360°

(3) Surface defects on lobes and journals

(4) Journal diameter, and a host of other variables

The gage disclosed is not limited to cams alone and can be used on othersimilar parts such as crankshafts, engine valves and the like, generallywhile the parts are rotating in place.

In addition, the invention discloses unique gages for the inspection ofquasi flat objects such as automotive body panels, pump vanes, chainlink side bars and the moving past the gage on conveyors.

Further disclosed are unique sensor arrangements containing miniaturehousings some with fiber optic transmission means.

An embodiment of one form of the invention is shown in FIG. 1. Acamshaft such as those used on a 4 cylinder automobile engine(diagramatically shown here for clarity, however, as having only twojournals and two lobes) is held on centers 5 and 6 with the center 5driven by motor 7 utilizing a fixture detail 20 picking up on the drivepin 30 of the camshaft.

At the particular point in time, an electro-optical sensor head 100according to the invention is positioned so as to inspect cam lobe 141.It is noted, that in this case the camshaft is shown having only twolobes 140 and 141 and two journals 150 and 151 even though in practicethere would be a much larger number of lobes and journals.

The sensor head is composed of light source unit 110 and sensor unit120. As shown the illuminating radiation 130 from the source unit isprojected across the cam lobe in profile. At a minimum, the sensor unitcomprises lens 145 which forms the image 146 of the lobe tangential edgeon photo diode array 148. The edge image so obtained on the photo diodearray moves up and down with rotation in an essentially equivalentmanner to that in which the lobe moves a flat faced follower such as ona hydraulic lifter.

Readout unit 160 analyzes the photo diode array output to find theposition of the lobe image and thence the lift contour as a function ofangle, with angular data provided by shaft encoder 170 located on thecam motor drive. Optional computer 162 compares the data so obtained,corrects it if necessary, to preset limits to arrive at an accept/rejectdecision.

In operation, the cam is rotated and at every degree, for example, asindicated by the shaft encoder, an array scan is made to determine thelift of the lobe at that particular angular position. When 360° ofrotation have been completed, the computer can then compare the dataobtained to the stored values for that cam lobe and accept or reject thecam based on that data.

In practice, there are many lobes on the cam that need such inspectionand the traversing means 180, shown schematically, is utilized toposition the ensemble of the sensor head and source unit (which may berigidly connected by bar 190) at each of the cam lobes in succession.

Typically a gage of this type would also include additional sensor unitswhere required to sense the journal diameters and possibly optionalsensing units to look for defects on the journals and lobes for example,using equipment as covered in co-pending application Ser. No. 15,792,filed Feb. 2, 1979, now U.S. Pat. No. 4,350,661, the disclosure of whichis herein incorporated by reference.

Machines such as this can be hand-loaded with the cams put into placeand the centers brought in or can alternatively be automatically loadedalong the lines of equipment shown in further embodiments. The gage isparticularly useful in the automatic loading form due to the fact thatit can operate fast enough and reliably enough to do all the cams of aplant on a production basis. This is a unique capability not previouslyavailable and vital if fuel economy and emission goals are to be met.

Speed of measurement coupled with accuracy and reliability is the veryessence of this embodiment of the invention. The very high reading rateof the system so described together with the non-contact, no wearoperation allows the reading of the lobe contours at much higherrotational rates than would ever be possible with the contact typemeasuring used heretofore. This allows one to measure each lobe within afraction of a second and thus complete a scan down an axis of a camshaftwhich may contain as many as 16 lobes and 5 journals (for a V8) andstill meet a production rate of approximately 150-200 parts/hr. This isessential if it is to be used in a modern high volume manufacturingplant. Such speed of measurement is at least twenty times faster thanany equivalent camshaft gage used heretofore.

A typical lobe section 210, shown in FIG. 2 is comprised by base circleregion 215 extending slightly more than 180° and concentric to the camaxis 216, max lift point 220, and open and closing ramp zones 225 and230.

The base circle region corresponds to the region of the circle where thevalve is closed and is critical if leakage is to be avoided, causingemissions. The ramp portions become critical primarily for fuel economyreasons.

Details of the sensor unit are shown in the side view of FIG. 2. Asshown in the figure, a light source, in this case, a diode laser, 300,produces divergent output radiation which is collimated by the lens 301and projected across the camshaft lobe, 210. The radiation passing bythe lobe (plus that reflected from the polished surface of the cam lobenear the tangential edge) passes through window 303 in housing 304 andis converged by positive lens 306 to form the image 308 on photo diodearray 309. This photo diode array may contain as many as 2,048 elements(the present maximum although it is envisioned larger ones will beavailable in the future) on 15 micron centers.

The movement of said image edge position 308 is monitored by readout 311to give an exact digital position of where the edge is. With the lensmagnification of 3:1 shown, the lift of the cam lobe (for example, 0.3inches maximum) then inscribes a 0.9 inch maximum movement on the diodearray which itself is 1.1 inches long approximately. Thus the lobeposition is kept on the diode array at all times.

For absolute maximum speed of response, the best currently availablephoto diode array is the Reticon 1872F having 0.030" wide elements andcapable of 20 MHz element to element scan rates (given its 1872 elements10,000 scans per second is possible although, in practice somewhat lessthan this is generally encountered). This means that taking data everydegree (which is generally more than ample) one can achieve a camshaftrotation speed of at least 1500 rpm! In practice there is seldom a needto go this fast but the capability is there.

Such high array speeds can allow one to achieve essentiallyinstantaneous results even at perfectly adequate rpm's of let us say 200to 300 rpm, using continuous light sources such as gas lasers and whitelight sources. However, it is of interest to consider utilization of apulsed light source such as the pulsed diode laser shown in the figureor, for that matter, a pulsed LED if sufficient power is available. Thepulsed source can be triggered to pulse every degree as an output of theshaft encoder with a pulse rate of 200 nsec. (diode laser) to 10 sec.(LED or Xenon strobe).

Such pulse operation "freezes" the image of the edge of the camshaft onthe diode array and allows the scan to read it out before the nextpulse. Thus the array can run at scan rates in the 1 KHz range, with noblurring and uncertainty due to the movement of the camshaft,particularly in the rapidly changing lift and falloff areas.Alternatively one can strobe the arays using special circuitry tocommence their scan as a function of the encoder position but thisrequires higher frequency response arrays with ample cw power.

As shown further in FIG. 2, there are other optical elements which areof use in such measurements. For example, the window 303 is almostalways used simply to protect the optics and to make it easy foroperators to clean since a certain dirt build up will affect thereadings.

Second, a stop 310, generally placed near the focus 307 of lens 306 isoften desirable to at least block the direct reflected waves from theleading edge of the camshaft. Also for depth of field enhancement, itmay be desirable also to block the diffracted waves as well using alower stop 310. It should be noted that depth of field to a degree isdesired because of the fact that the cam lobe runs out relative to thecenterline of the camshaft established in this case by centers 320 and321.

Also of value may be a second lens 316 to provide a substantial opticalmagnification in a smaller package or conversely to provide the classictelecentric lens system used for maximum depth of field.

Also an optional cylinder lens 317 may also be used to further convergelight along the axis of the cam onto the diode arary. The reason forthis is that the diode array size even with the 0.030 inch wide elementsof the 1872F (which has some of the largest width elements obtainable)still with 3:1 magnification is only covering a zone 0.010" on thesurface of the cam in the axial direction (`w` in the diagram). Sincethe light field is typically much broader than this as is the cam lobeitself, it is obvious that it may be desirable to look at a largerlength of the cam lobe to improve the power density onto the diode arrayas well as to make this system relatively less sensitive to minor nicks,dirt, etc. on the lobe if any. This is, of course, particularly true ifdiode arrays having smaller width elements are used. For example theReticon 1728G with elements approximately 0.001 inch wide.

Other optical elements that may be of use are auxilliary detector 331used to monitor the light power (not blocked by the cam lobe (ie. in thezone above the max lift position). These elements, when provided at thesensor side as shown actually monitor the power actually transmittedthrough. The power monitor is then used as a compensation signal forwindow dirtyness, light power degredation and light power erracticnesswhich can occur with pulsed systems which then is used in the circuitryshown below. All in all, a very valuable addition.

While it is envisioned that a primary use of this invention will be toinspect the total lift contour, the lobe 360° including all regions ofthe cam, there are several checks also possible with the invention whichcan be done at less cost (since far fewer data points are required).These are base circle runout (typically allowed to be 0.001", max.), maxlift and phasing of max lift to dowel pin or number of lobe. Somewhatmore difficult is rate of lift error in the ramp zones, eg. 0.0001"deviation from true over a 10° zone.

The invention can also check chatter on any of the portions by comparingthe high frequency rate of change of position. To do this digitally,however, requires a high data rate since readings are desirably everyhalf degree or better. It is also possible to do it analog fashion byband pass filtering of the output of a single analog detector positionedto see the same light field as array 309 and looking for high frequencycomponents indicative of chatter (typically periodic).

It is noted that to check base circle, much less range is required,typically 0.010" max, making a simpler sensor unit. Max lift and phasingcan typically also be done with similar low range sensors, mounted,however, at a different location (ie. centerline 0.300" above basecircle sensor centerline).

Let us consider now the magnification required of the system. Since thetypical automotive camshaft lobe lifts are in the range 0.25 to 0.3inches, it is clear that the maximum length of diode array availabletoday of about 1.1 inches in length then means that an opticalmagnification at least using a single diode array system, of no morethan approximately 3 or 4:1 can be utilized. Such magnification iseasily obtained with common high quality enlarging lenses and if goodlenses are utilized the total magnification is virtually linear over theentire range of lift. Any non linearities if they are present, can becompensated in the computer by simply storing the values obtained from amaster cam of known dimension and correcting the values obtained inpractice. Such a correction which utilizes a built-up table of valuesactually takes no more time since it is simply the corrected values thatare used for the comparison points rather than the values taken off theblueprint. Naturally, for this technique to work, any sensornon-linearity must be repeatable but this is generally true given thesame lens system and the same light field both of which are virtuallyinvariant. Some precaution has to be made with the light fields frompulsed diode lasers but generally this can be sufficiently invarient tomake such a plan effective.

Returning to the question of magnification unless larger arrays becomeavailable or multiple arrays are used, it is clear that no more than 4:1can be utilized optically and it is of course noted that at 4:1 theimage is quite clear. A typical diode array output is shown in FIG. 4.As can be seen, this shows a sequence of detector elements of such an1872F array the elements being numbered 1 through `n` respectively whichare all in the lighted zone of the light field at which time the edge ofthe cam is appeared and the zone decreases to dark very rapidly withinthe space of approximately 2 elements. The exact slope of the curvedepends, of course, on the system depth of focus and the location of thepart edge. If telecentric systems are used, more elements are containedwithin the edge image, although less variation in the number of elementsis obtained throughout the rotation.

At a 4:1 magnification, it is clear that with a 16 micron center tocenter spacing, each element of the diode array is reading in liftincrements 4 microns. Since resolution of generally 2 to 4 times thisamount is desirable in inspecting camshafts, a question comes up how toachieve this. Resolution of 1 micron is achieved in this instance byutilizing a 4 times threshold circuit which functionally operates asfollows.

Since 4X electronic multiplication is desired, levels are utilized,levels 1, 2, 3 and 4 with four level 4 being the level closest to the 15volt typical saturation voltage of the silicon detectors. In this case,it has been desired to drive all of the detectors into saturationalthough not too far. The levels are then set up up to the 15 volt rangefor example, at 3, 6, 9 and 12 volts respectively.

The answer then is obtained using the equation below wherein the numberof lit detectors is equal to the sum of the detectors of the arraycrossing each level divided by 4, ##EQU1##

In the example shown, a continuous row of `N` detectors have outputsabove threshold voltage level 4, N+1 are above level 3, N+1 above level2 and N+2 above level 1.

As can be seen in the example shown, the number is equal to the numberof detectors crossing the top level, level 4, plus 3/4. In other wordsthe system has resolved to essentially within 1/4 of a detector therebyessentially enhancing the packing density of the array by a factor of 4.For such a circuit to function well it is necessary that the power bestabilized to at least the level of multiplication required (eg. 1 partin 4). This can be accomplished using the auxilliary detector 331 whichis used to set up the threshold levels as a function of input lightpower. Generally speaking, such a level detection circuit is practicableup to approximately 10 times, beyond which differences in the individualdetector sensitivities etc. can start making the answer less and lesstrustworthy. It should be noted, of course, that the resolution obtainedcan be extremely high; for example 0.4 microns or 16 millionths of aninch at a factor of 10 times with 4× optical magnification.

Basically this sensor is all digital from the diode array although thelast detection of the levels is obviously done on a quasi analog basisand any drift in the levels can manifest itself in a changed answer.This again is another reason for not trying to push the level ofdetection beyond a factor of roughly 10.

Clearly it is the ability of the sensor head to take very highresolution measurements at a high data rate that allows this machine tohave the specifications that it does. However, the rest of the parts ofthe machine are also valuable in applying this invention in practice.For example, in order for it to check cams on a production basis atrates of one every 20 seconds or less, it is necessary to have thefollowing components:

(1) A means to move the cams into position. This is actually optional asthe cams could be hand-loaded into the machine but generally a fullautomatic machine is desirable. The typical movement device is a walkingbeam transfer.

(2) A means to pick the cams up off the walking beam.

(3) A means to revolve the camshaft at the rated measurement speed whichis typically 60 to 300 rpm depending on part rate, number of lobes andjournals to be inspected etc.

(4) Means to scan the sensor head down the length of the cam togetherwith control means to cause the readings to be taken at certain axiallocations down the length of the cam.

(5) Encoder and pickup means to encode the rotational position of thecam relative to a feature such as a dowel pin or hole on the end of thecam that is used for timing.

(6) The sensor means used to take the data

(7) Readout and analysis means such as microcomputer(s) to analyze thedata and make the accept/reject decision.

Typically, additional equipment utilized are marking means to mark thedefects of the cams and, in some cases, what is wrong with them andreject means to direct the bad cams from the production stream.

Similar points required to make the described fully automatic systemwork are now mentioned. For example, the computer system not only mustcompare the data to stored values, but if the part is fixtured oncenters the computer must correct for the natural bow in the cam whichis not desired in the lift answer. This can involve considerableprograming and generally requires two microcomputers to be used, one tocontrol and read data from the sensor head into the memory plus a secondto simultaneously operate on the data obtained from the previouscamshaft. Such correction, of course, is not required for bow if the camis located with the journals clamped which trades mechanical complexityfor the computer.

A FIG. 5 illustrates too how a typical sensor head can be placed overthe automation. In this case an inverted "U" shape housing 500 ismounted on motorized slide 501 which moves it down the axis of the camas described above. In the housing are two light sources 510 and 511, ofthe type described in FIG. 2 and 3 above illuminating the cam throughwindow 512 and a sensor head 513 viewing through mirror 514 the camlobes also typically as described above. In the case depicted, a furthersensor head is used to sense the bottom edge of the journal, 515. Thetop of the journal, diametrally opposed, is sensed with the main lobesensor, 513. It is noted that this sensing of the journal top and thecam lobes is possible because journals are typically at almost the sameradial position from the cam axis as the max lift point of the camlobes.

Also shown on this particular sketch is a transfer means 503 typicallyof the "walking beam" or "lift and carry" type to move the cams into thecam gage pick-up position and lift means 504 to lift the cams out of thetransfer up into the actual gaging station, where in this case the camis picked up on centers and rotated.

When the gaging is over, the centers retract and lift means 504 lowersthe part back down onto the walking beam. The cam then is transfered outto an idle station and thence to a reject or accept track further ondown the line.

Such an arrangement has proven to be an excellent way to transfer thecams through, gage them and move them out without the difficultmechanical contacts and crash possibilities of normal camshaft gaging.

Under certain conditions, it may be necessary to simultaneouslydetermine the radial location of the two end journals while the cam isbeing rotated between centers. This can be accomplished by two sensorsof the type 513/515. Checking the radial runout of these journals allowsone to correct for possible eccentricity in the cam due to imperfectspindles, centers and the like. The reason for doing this is that one isessentially assuming the cam rotates in a repeatably time varyingmanner, and if this is not the case, it is necessary to monitor the twoend journals as a function of 360° rotation and compare the otherjournals to them in order to develop the profile of the camshaft anddetermine the true centerline of the cam at all times such as the datacan be compared.

There are some very positive features about this system which are notpresent in other optically based systems that may have been used in thepast on camshafts. For example, the accuracy is sufficient to make themeasurements in a manner that can be useful since the sensor unit is anall digital device and capable of extreme long term stability with nodrift etc. Another feature is, of course, that the data rate taken bythis device can be high enough on the order of 1,000 or moremeasurements per second to allow an effectively high camshaft scan rateto be obtained. For example, if the scan rate of the sensor was only 100readings per second, and one which to read 360° around the camshaft,this would then require 3 seconds or greater simply to do one lobe.

It is of interest now to consider the dynamics of this system. Forexample, if one is inspecting a four cylinder camshaft, there aretypically five journals and eight lobes each of which have to beinspected or a minimum of 13 axial locations of interest. Typically,however, one may also wish to get the taper off the journals and lobeswhich add another 13 points, and in many camshafts one may also look atthe runout of the fuel pump eccentric if there is one, the pump gearrunouts and other features using additional sensor heads which will befurther described. These may include the thrust runout of the camshaftthrust face and the surface defects on the lobes and journals thatcannot be seen as a function of dimension.

Where the number of features are limited as in the 13 of a basic 4cylinder cam measure, the gage can be set up easily to dwell at each ofthe points while still maintaining the normal production run time of 15to 20 second cycle or greater in Europe.

For a typical camshaft 15 inches long and rotating at 300 rpm, thismeans that one would use up 3 seconds of the scan in looking at let ussay, up to 15 features, plus approximately 5 seconds in making theactual travel between lobes in the incremental steps or a total of an 8second scan time. This, coupled with a typical transfer time of 6seconds, yields a gage cycle of 14 seconds, which is perfectlyacceptable.

However, as the number of features grow, it is obvious that one cannotafford the dwell time in this system and one then must consider thesensing of the camshafts while the sensor is moving. This involvesfiguring the taper of the camshaft lobe data into the actual equationsfor the lobe contours a function of rotation. Another alternative is theuse of multiple sensor heads operating in parallel, discussed below.

Where speeds have to be maintained even higher, for example, if all thetapers are desired, it may be necessary to use a dual headed sensor. Inthis case, two heads spaced at half the cam length are utilized and eachone is asked only to take data over half the length of the cam. If theseare moved under independent motion, it is clear that the effective scantime can be cut in half and with slightly worse results if one movesthem together which means certain ones may have to be idle while theother measure if the lobes and journals are not equally spaced.

If this is required it may be necessary to use individual sensors foreach lobe and journal. Naturally two are required for the journalswhereas only one of much larger range for the lobes.

An example illustrating this case is shown in FIG. 6 and of particularinterest in this illustration is a simplified sensor head which can beimplemented for this particular application. It is noted that thissensor head must be of sufficiently small size to be packed in closeenough to do the lobes unless complicated mirror systems etc. areutilized.

Essentially two sizes are envisioned, the first using a small diodearray of 256 elements or less necessary only to see the journals andbase circle regions of the cams (if the total lobe contour is not ofinterest). The second version has a larger diode array typically between1700 and 2100 elements and used for the total lift. These versions arealso well suited to inspection of other parts as well, such ascrankshaft journals, pistons and the like.

Both units are shown in essentially cylindrically symetric housings. Thelight source unit 550 is located in Vee block 552 and the sensor units555 located in Vee block 556. Both locating blocks are optionallyconnected using optional bar 560. The sensor and light source unitsutilize cylindrical housings 565 and 566 respectively. Internally, bothunits are similar to those described above. The cylindrical housing iseasy to mount in Vee blocks, which makes for easy lineup andreplacement. The housing utilized is generally only large enough toincorporate the particular diode array utilized, 570, with lens 571 tomatch. For example, the Reticon 256C array can be accommodated within ahousing size of 0.75 inches which is small enough to be packed in oneach lobe of a typical camshaft for example. The lens 571 is put in fromthe front with optional window 572 and power monitor detector 573 andlens stop 574.

For larger arrays, a housing size of two inches is required. Arectangular box can be utilized or a mirror system is required toaccommodate their placement since the center to center spacing of thelobes is typically 0.8 inches.

Note that the diode array is mounted directly to the steel portion ofthe housing and not to flimsy circuit board that has been commonly usedin practice previously. This is necessitated because of the precisionwith which sensor systems such as this are utilized.

With the array mounted thusly and the limited sensor box size available,it is generally desirable to mount the circuit cards 580 which drive thearray in an external card rack 581 located as nearby as possible(because of the problems in high speed signals over long lines). Wherepossible these can be clustered together into one rack for servingmultiple sensors. If necessary one rack per sensor can be used.

Obviously, other box arrangements could be utilized which would allowthe large diode arrays to be used without the mirror. In short theywould have essentially non cylindrical box housings where the arraycould extend in the vertical axis.

Naturally the use of such multiple sensor heads provides the fastestpossible part rate. Generally a cost disadvantage is incurred in thecamshaft gage where large numbers of high range sensors are required. Itcan, however, be the best solution if the high speeds and utmostreliability are required since no mechanical motion is utilized.

It should be noted, however, that the mechanical motion of moving thesensor head down the camshaft axis has a valuable feature in providing adegree of programability between different camshafts. In short, tochange camshafts it is only necessary to program in the different datapoints with which to make a comparison as well as the different axiallocations where the sensor head should take its readings and too amaster block can be read each cycle to verify a gage operator.

This allows a very interesting feature of the scanning type approach isthat in one can actually intermix camshafts on the same line. Theinvention contains the further provision of providing a sensor such asin FIG. 5 to observe from a mark placed on the cam which cam is beinggaged and adjust either the data and perhaps the axial locations andeven the drive positions of the motor driven slides to accommodate thatcamshaft. It is not, for example, out of line to even includepossibility of intermixing V6 and 4 cylinder camshafts on the samemachine!

The forgoing discussion has been primarily directed at the inspection ofcamshafts which is certainly the most necessary in terms of thecamshaft's tremendous influence on fuel economy and emissions, and too,the invention here disclosed offers the only known really good way of100% inspecting all of a plant's production in this regard.

However, the concepts herein and embodiments can be extended to otherparts of cylindrical symetry besides camshafts. The easiest extension isindeed the crankshaft which, while there is no need to sense over theranges required for the cam lobes, there are the journals and the pinsand the fillet contours which can be sensed using sensors of exactly thesame type. Indeed one of the interesting features is to gage thejournals of the crankshaft and simply move the nest of sensors slightlyso as to get into the fillet area of the crank and contour it.

It should be noted that when gaging the journals, the base circles orthe crankshaft journals, for example, that a ordinary white light suchas a tail lamp can provide ample illumination replacing the diode laserin FIG. 2. And too there is no particular requirement to pulse in thesezones since there is not a rapid change of shape or a depth of field. Ingeneral, simpler lens systems can also be used since there is no need todeal with the depth of field that occurs on the cam.

Next consider the case of inspection of crankshafts according to theinvention. First, it is clear that the sensor arrangements used forcamshaft journals described above can also be used on crankshaft mainbearing journals, hubs, gear fit diameters, posts and other importantcrankshaft dimensions whose diameters are centered on the axis ofrotation. The same sensor, transfer and lift arrangement shown in FIG. 5is indeed ideal, although usually it is desirable to employ separatesensors as described above. Those should have sufficient standoff toclear the crank pin orbits on rotation.

For the crank pin diameters a separate pair of sensors for each diametercan be used located so as to view the pin at some point in its orbit,generally at top dead center. Since measurement can be taken on the flyaccording to the invention there is very desirably no need to stop thecrank rotation to gage the pins, or to even locate the crankcircumferentially since the sensor unit can be programed to read onlywhen the pin diameter image is in its field of view.

Shown in FIG. 7a is an alternative embodiment of the sensor head whichobviates the requirement for placing the circuit cards near the sensorplus provides a smaller sensor housing dimension. In this case a pair oflight sources 600 and 601 illuminate for example the opposite edges 605and 606 of crankshaft pin journal 608 as it revolves about axis 609.Sensing occurs when a signal from detector 610 indicates that the pinjournal is in the correct position, typically top dead center as shown.

A pair of sensor units 611 and 612, comprised of a housing 613containing lens 614 and fiber optic light conveying means 615 whichcarries the image of the part edge back to a remotely located diodearray 620 in readout box 621. Optionally the light sources can also becomprised of remote light source such as LED 622 conveying light throughfiber 623 which is then colimated by lens 624. Plates 616 and 617 holdthe sources and sensors in alignment. Optional windows 618 and 619 arealso provided.

In this example two types of fiber conveying means can be utilized:Coherent fiber bundles and single fiber wave guides such as Selfoc longlaser guide. The first case has been illustrated above wherein lenssystem 614 focuses a magnified image of the part edge onto the fiberbundle end and output lens 625 focuses the end of the bundle onto thediode array.

A second version illustrated in FIG. 7b utilizes a single waveguidefiber 630 at the approximate focus of object lens 631 (typically 25 mmfocal length), both in housing 632. At the output, diverging field 633can be directly read by diode array 634 or further imaged and magnifiedby lens 635.

A feature of the wave guide fiber is simplicity, potential low cost,smaller size and the much higher image quality since it is a singlemedium behaving like a lens. This also means that it is not necessary tomagnify the image presented to the fiber to avoid interstitial problemsand accordingly simple fiber end matching sensor and larger standoffs tothe part can be used. This is particularly valuable in this crankshaftexample where one wishes to clear the pin orbit while maintaining highresolution.

Another feature of this embodiment is that a single diode array andcircuitry can service multiple sensor heads. For example, in FIG. 7a, asingle lens 625 is shown imaging outputs from fibers from both pinjournal edge sensors. Signal processing is adjusted accordingly to findeach image.

It is noted that a series of remote LED light sources can be pulsed insuccession one for each sensor. This automatically causes only one imageon the array at a time. Alternatively a single white light bulb forexample can illuminate multiple fibers at once, implying reduced price.

The fiber approach has many advantages including ease of design andmanufacture. It is, however, difficult to use in cases where utmostrange or resolution are required.

The gage microcomputer and other array readout circuits are desireablyco-located with the array and fiber termination. Light source(s) 622 canalso be located there as well to provide a total self contained package.

Note that since a crankshaft gage according to the invention typicallyemploys 30-50 such sensor heads (for main and pin journals, hubs mainsetc.) it is desirable to protect the whole ensemble of sensors(extending in and out of the plane of the figure) with plate glasswindows 645 and 646. These seal up the total light source herein 648 andsensor housing 647 and also are easy to clean--an important feature in aplant.

It is noted that the concepts described herein can also be used to checkrough castings of cam cranks and other parts before machining therebypreventing machine damage and helping to insure good finished parts

FIG. 8 illustrates another construction of the sensor housing suitableto close packing and large range. In the example shown, three sensorsaccording to the invention 650, 651 and 652 are arranged so as to sensethe diameter and relative contour (ie. bow) runout of an engine valvestem 655 when the valve is rotated in vee rollers 660 and 661. Transfermeans 666 comprising chain or walking beam moves valves in and out ofthe roller fixture as in FIG. 5 above.

In a gage of this type it is desired to have large sensor range toaccommodate multiple valve diameters, while also having high resolution(typically 50 millionths of an inch) and small package size particularlyin the width or direction along the valve axis. This allows the sensorsto be easily repositioned axially for different valve types. Suchrequirements are similar to those of the camshafts and crankshafts notedabove but in this case it is also desirable to image both edges of thevalve diameter on the same diode array using a single lens. This makesfor the most compact and lowest cost package, but is simply not feasiblewith larger parts due to their larger diameters.

The sensor housing for example that of sensor 650, is desirablyconstructed using steel base plate 670, typically 0.2" wide by 6" longand 1/4" thick to which the objective lens 671 in mount 672, and diodearray 673 in mount 674 are attached. In this case, a two lens system isutilized also incorporating a negative system lens 680 in mount 681which allows maximum standoff to the part while still remaining opticalmagnification in the required 2:1 to 5:1 range. Additional 2× to 10×magnification is obtained electronically using circuitry as described.As above, compensating detector is often desirable.

The cover, not shown for clarity, seals the sensor from the outside anda window is also useful for this purpose (unless all sensors in thegroup are situated behind a single easy to clean plate glass such as691.

Clearly the light sources can also be constructed in similar housingshousing base plates, mounts and formed covers. However, in this examplea long linear light source is shown, 690, extending the length of theobserved area of the part. This allows easy mounting and replacement andis typically also covered by plate window 691 for protection. Ifrequired a stop can be used in the lens system to accept only quasiparallel light from this source, otherwise diffuse. However, depth offield in such a fixtured valve rotation example is seldom a problem asthe part is of high tolerance.

The sensor housing incorporates dowel pins 696 (shown on base of sensor652, for clarity) to allow easy repositioning into mounts such as 697for part changeover. Alternatively micrometer slide mounts can beprovided, such as 698 on sensor 651 to move the head to a new location.Such movement can even be motorized on command using a stepping motor,thus providing full electronically commanded changeover for differentvalves. It is noted that the use of the long lamp 690 is advantageous inthat no repositioning of the light source is required for each valvesize.

For further inspecting valves several other similar sensor are alsodesirable. For example, axial scanning ones 700 (shown along line ofviewing) to sense the gage line on the valve seat and 701 to measure thefoot and location. Another two may be employed to sense the headdiameter and runout and 704 to sense keeper groove diameter and runout.(Runout is determined by looking at the location deviation on one edgealone during rotation.) Note provision of stop 705 to rest foot againstduring rotation by rubber roller drive means not shown for clarity.

FIG. 9 illustrates another embodiment of the invention utilized to sensethe shape of parts conveyed past a "nest" of sensor heads according tothe invention.

In this context it is of interest to observe that the valves shown inFIG. 8 could be moving in the z direction, with their diameter andrelative bow dimension in one plane measured on-the-fly (using highspeed arrays or pulsed sources as above) as they were transfered throughthe sensor field. Such measurement would allow a much faster rate thanthe 4000/hr maximum capable when a rotation in place is necessary for360° inspection.

Such an example, shown in FIG. 9, is illustrated relative to aquasi-flat part, namely a transmission pump vane 709, whose outer edgepoints 710-719 are measured using a nest of photo diode arrays 730-739mounted to steel plate 728. In this case, because of the part smallsize, (eg. 1" square) a single lens 725 is used, to form the part edgeimage 726 on the arrays. Diode array circuit cards are in a separaterack not shown above plate 728.

In operation, the part is fed from a feeder not shown down Teflon Track740 past the sensor group or "nest". When the part trailing edge issensed to be in position using sensor diode 750 with slit 751 and LEDlight source 752, the light 760 is pulsed to illuminate the part edgeand freeze it on the diode arrays for measurement. Appropriate holes arecut in the track bottom to allow the light to pass through at themeasuring locations.

Where resolution requirements are not stringent, a pulsed Xenon lamp canbe used to illuminate the part, using a diffuser screen or collimatinglens between it and the part.

However, in the case shown, the resolution desired is 1 micron, and thisrequires very short pulse widths and a high degree collimation to freezethe part and provide a decent light field. Accordingly it was desired inthis case to use a nest of pulsed diode lasers (not shown for clarity)having 200 nsec. pulse widths to illuminate the edge points 710-719.Each diode laser utilized an individual lens to collimate its output.

To further provide accurate measurement of the part length and width atvarious sections, plus provide a calculated value for straightness andsquareness of the edges, a micro computer 765 is utilized to compute andcompare defected edge points from arrays 730-739 and further utilizethis data to correct for skewness of the part in the track. This istypically a small cosine error since the part is retained within 0.010"or better by the track side rails 741.

The microcomputer can obtain the requisite data for part acceptance orreject before the part reaches the reject gage 770 10" away. Incredibly,this system can check 30,000 parts per hour, feeder permitting, and is10 times faster than any gage used previously. A direct increase inproductivity of 1000%. Furthermore, because of the non-contactoperation, it is virtually jam proof.

Note that a metering wheel 775 driven by motor 776 is often desirable onthe track to regulate the speed of the sliding parts within a certainband.

The diode arrays used in this case were Reticon 256C's having 0.001"center to center spacing. A 10x lens magnification was used via a 50 mmCanon F 1.4 lens and a 4× electronic multiplication as described aboveto obtain 25 microinch resolution of part edge dimension.

In the above example, it is often desirable to replace track 740 withconstant speed moving belt such as those of FIG. 10. For example, shownin FIG. 10A a transparent plastic belt 780 is used in which Xenon strobelamp 781 illuminates chain link side bar 782 in profile on command ofpart present sensor such as 750 previously and not shown for clarity,and freezes its image, formed by lens 784, on matrix type diode array785 in this case a GE TN 2500 having 250 adjacent lines of 250 elementseach on 0.001" centers approximately.

As in all other optical gages here disclosed, a window 786 is desirablyused to protect the sensor, itself in air tight enclosure 787.

As in other embodiments it is desirable also to compensate for dirtywindows and light source degradation. In this particular case it is alsonecessary to compensate for dirt etc. on the transparent belt 780. Toaccomplish compensation, a detector 788 is utilized coupled to aThyrister flash circuit 789 to turn the flash off when the detectorcircuit has seen a standard amount of light. This is a simple yetelegant solution.

Also desirable is a blow-off or wipe-off 791 to clean debris off thebelt, on the return pass.

Another desirable belt arrangement is shown in FIG. 10B. In this caseonly part outer diameter dimensions are required and an opaque belt 800can be used. The belt conveys cylindrical wrist pin 801 past the sensorunit as before, but it is noted that in this case the belt is slightlyless in width than the part diameter D. This allows the edges 805 and806 to be seen when the part is guided by guides 808 and 809. Acontinuous light source 810 and dual linear array sensor, 811 (inset)can be used to profile the wrist pin and obtain its largest diameter,taper, etc.

As shown the continuous light source of this example is provided bycontinuous diode lasers 815 and 816, with collimating lenses 817 and818. Images are formed by lenses 820 and 821 on linear diode arrays 822and 823. Typically 10x magnification is utilized where high toleranceparts are inspected such as wrist pins. Windows 830 and 831 are providedon the light source and sensor housings, 832 and 833.

The transparent belt above offers considerably more flexibility in thata large variation in part size can be accommodated just by changing theside guides and the sensor readout program, limits or magnification asrequired.

Before continuing, it is of interest to consider the use of the marixarray of FIG. 10. Clearly one flash is all that is required to freezethe total part image on the array from which it is readout, digitizedand compared before the next part arrives.

Of considerable importance in actually using a matrix array system inthis fashion is that the resolution requirements are often quite highrelative to the number of detectors available in any one line. Statedanother way, a 1"×3/4" chain link side bar can on the face of it only beresolved to at best 0.004" in any dimension if a 250×250 element arrayis asked to look at the whole part image. This too assumes perfecttriggering by the part present sensor.

Accordingly, it is desirable to orient the scan lines of the matrixarray perpendicular to the direction of motion such that the maindimensions of interest, e.g. part diameter, part width, thread form etc.are scanned sequentially. Then a count multiying circuit such asdescribed in FIG. 4 above can be utilized to increase the sensitivity ofeach scan. This then can give the array system a resolution of up to 10×greater in the direction of the scan (in this example that transvers topart motion).

Another item of interest is that reflective illumination can also beutilized, rather than the profile types shown. For example, in FIG. 10Aconsider that the flash guns were located in a position above the belt

which now could be opaque. In this case, the compensation detector andcircuit also helps compensate for part reflectivity variation.

This same reflective illumination can be used with other embodiments.However, image quality is always better if the part edges can be seen inprofile, rather than in reflection.

Note that belt can be dark (e.g. black rubber) in which case the partitself provides the predominant light reflected. Alternatively, the beltcan be reflective (either diffusely or specular--depends on light sourceto--sensor angle) such that the belt reflection is stronger than thatfrom the part, in which case the effect is like profile illuminationfrom below.

It should also be noted that the count multiplication techniquedescribed can also be used to improve the performance of circular diodearrays for example the Reticon 720C. This array can be placed in theapparatus of FIG. 10A for example to determine the angular center tocenter spacing of holes in a bolt circle on a part conveyed on atransparent belt as shown, or in reflection.

A further embodiment is shown in FIG. 11, where a group of sensorsaccording to the invention is utilized to determine the outline of anautomotive sheet metal panel assembly in this case a door. Determinationof outline dimensions is essential if the door is to fit correctly intothe finished body. Data taken from such an inspection is typically fedback to welding operations to correct fixture locations etc.

This example illustrates the use of pre alligned sensor packages versusseparated source and sensor units, measurement fixtured parts oron-the-fly and use of additional triangulation sensors to establishdynamic reference points and perform additional measurement of sheetface contour points rather than just door outline.

FIG. 11 door 840 is moved by rollers 841 into the gage 843 comprised bydiode array sensors 850-855 and associated light sources used todetermine the outline of the door (typically as many as 20 such sensorscan be used). In a first mode, similar to that of FIG. 9 above,mesurement is made on-the-fly by using optical part present sensor 860to determine the part is in position and trigger the sensors 850-855 toreadout their outputs into readout and microcomputer control 861.

A complication in this case arises because part shape is somewhatirregular and location cannot be well constrained as with the guidesused in the track or belt used for the pump vanes etc. described above.In addition, three dimensional coordinates, rather two dimensionaloutlines are also required in certain instances, yielding anothervariable to be controlled.

There are two solutions to the location problem. First, physicallocators can be used such as steps 870, 871, 872 and 873 (dotted lines).The stops, actuated by cylinders, solenoids etc. This solution, however,requires the part to be stopped and considerable further mechanicalcomplexity.

The second idea is to utilize other sensors according to this inventionplus triangulating types such as 880 and 881 also described in copendingapplication Ser. No. 34,278, now U.S. Pat. No. 4,373,804 the disclosureof which is herein incorporated by reference, to dynamically establishthe coordinate reference simultaneous with the measurement. In thisarrangement it is noted that the light sources and sensors used tolocate and determine door coordinates must be positioned so as to clearthe path of the door and must be able to effectively operateinstantaneously on command of the part present signal.

Note that the count enhancement technique shown in FIG. 4 is furtherbenefited by having a circuit operating at a low threshold voltage (e.g.below level 1) which looks for the edge. When it finds it, it then looksat the maximum voltage of any detectors nearby and sets up the thresholdlevels 1-4 from that. In addition only count deviation from the 1stdetected count is derived, so as to determine edge location. In thisway, a badly variant light field still does not influence the readings(an important point in practice).

Due to the limitation of the finite size of elements in diode arrays,the position of an edge of image cannot be detected to a greateraccuracy than one element, when conventional means of detection areutilized. However, when using interpolation between elements, theresulting improvement in accuracy is only limited by the quality of thediode array.

FIG. 13 shows the video output with an edge focussed on the array. Thetransition from dark to light is gradual, even with a well focussedimage. This fact allows the interpolation process to take place bytaking into account the illumination levels on the array elements in thetransition zone. By setting, for example, four threshold levels anddetecting the video against these levels, the mid-point of thetransition can be found to an accuracy equal to one fourth the elementto element distance.

A circuit for automatically, continuously interpolating the video outputis shown in FIG. 12. The video signal is fed to four similar leveldetectors (902-905) by a video buffer (901). Level detectors (902-905)can be a conventional differential operational amplifier such as an LM301 and video buffer can be a conventional operational amplifier such asan LF 356. The threshold levels are set by a voltage dividing resistorchain comprising resistors R901, R902, R903, R904 and can be adjusted bya variable resistor R905. The ratios of the voltages are set byselecting the appropriate resistor values. The output of each leveldetector is fed to the clock inputs of conventional D-type flip-flops906, 907, 908, 909 (such as integrated circuit 7474). The respective Qoutputs of flip-flops 906-909 are interrogated cyclically in sequence bya digital multiplexer 910 (such as integrated circuit 74153) that issequentially clocked by a binary counter 911. Binary counter 911 can bea conventional integrated circuit 7493 that is clocked at a frequencyfour times higher than the array frequency with the two frequenciesbeing synchronized.

The count out output from multiplexer 910 is in a form of a pulse trainwhich we call count output. This output would normally be fed to thecount input of a totalizing counter (not shown).

At the beginning of each scan flip-flops 906-909 are reset and duringthe scan time, when the video signal reaches a threshold level, theappropriate one or ones of the flip-flops is or are set. Thecontinuously scanning multiplexer 910 produces a count pulse for eachflip-flop that has been set high on each of the scan sequences.

I claim:
 1. Apparatus for inspecting a workpiececomprising:electro-optical sensor means for sensing the positions of aplurality of edge portions of a workpiece in an inspection location,said electro-optical sensor means comprising:light source means forilluminating a plurality of edge portions of a workpiece in saidinspection location; lens means for forming an image of each of saidilluminated edge portions; and a plurality of photosensitive arrays,each array comprising a plurality of light sensitive elements capable ofproducing an electrical signal in response to light incident thereon,each array being positioned to receive an image of a respectiveilluminated edge portion of a workpiece; means for analyzing the signalsfrom said light sensitive elements to determine a dimension of saidworkpiece; and further sensor means for determining the position of aworkpiece in said inspection location, said further sensor meanscomprisinglight source means for illuminating a plurality of knownportions of a workpiece in said inspection location, lens means forforming an image of each of said illuminated known portions and aplurality of photosensitive arrays, each array comprising a plurality oflight sensitive elements capable of producing a signal in response tolight incident thereon, each of said arrays being positioned to receivean image of a respective illuminated known portion of said workpiece insaid inspection location, and means for analyzing the signals from saidlight sensitive elements of said further sensor means to determine theposition of a workpiece in said inspection location.
 2. Apparatusaccording to claim 1 further comprising means for moving a workpiecethrough said inspection location.
 3. Apparatus according to claim 2wherein said light source means of said sensor means and said lightsource means of said further sensor means each comprise means forpulsing the light to freeze the images of respective illuminatedportions of said workpiece in the respective photosensitive arrays ofsaid sensor means and said further sensor means.
 4. A method forinspecting a workpiece comprising:illuminating a plurality of edgeportions of a workpiece in an inspection location; forming an image, bylens means, of each of said illuminated edge portions; imaging each ofsaid illuminated edge portions onto an individual discretephotosensitive array of a plurality of discrete photosensitive arrays,each said discrete array comprising a plurality of light sensitiveelements capable of producing an electrical signal in response to lightincident thereon; analyzing the signals from said light sensitiveelements to determine a dimension of said workpiece; and determining theposition of a workpiece in said inspection location, said positiondetermining comprising illuminating a plurality of known portions of aworkpiece in said inspection location, imaging each of said illuminatedknown portions on a photosensitive array comprising a plurality of lightsensitive elements capable of producing a further signal in response tolight incident thereon, and analyzing the further signals from the lightsensitive elements to determine the position of a workpiece in saidinspection location.
 5. A method according to claim 4 further comprisingmoving said workpiece through said inspection location, and wherein saidillumination of said edge portions and said known portions of saidworkpiece each comprise pulsing the light to freeze the images of thesaid edge portions and known portions on the respective photosensitivearrays as the workpiece is moved through said inspection location.